Furnace wall blower improvement



p 1966 E. P. PETIT FURNACE WALL BLOWER IMPROVEMENT 2 Sheets-Sheet 2Filed Oct. 20, 1964 United States Patent M 3,273,543 FURNACE WALL BLQWERIMPROVEMENT Elwood P. Petit, Windsor, Conm, assignor to CombustionEngineering, line, Windsor, (301111., a corporation of Delaware FiledOct. 20, 1964, Ser. No. 405,167 17 Claims. (Cl. 122-392) My inventionrelates to furnace wall deslagging and in particular to a method andapparatus for improving the effectiveness of short retractable typerotating wall blowers.

When an ash bearing fuel is burned in the furnace of a vapor generator aportion of the ash particles in the fuel deposit on the furnace walltubes. This ash tends to build up on these walls forming a layer of ashand slag. This layer insulates the furnace walls, which disturbs thebalance of heat absorption throughout the unit and also has adetrimental effect on the efliciency of the vapor generator.

Throughout the furnace the metal temperature of the Wall tubing is muchlower than any known ash softening temperature and consequently the ashadjacent to the tube surface must be solid. Conversely, the gastemperatures within the furnace generally exceed the ash softeningtemperature and the temperatures within the burner zone of an ordinaryvapor generator always exceed the ash softening temperature. While theface of the slag layer which is adjacent the tubing approaches thetemperature of the furnace wall tubing, the other face of the slag layerwhich is adjacent the furnace cavity approaches the gas temperature.Therefore, running slag can be anticipated throughout the furnace andparticularly in the burner zone, where there tends to be a very highheat absorption rate in the furnace wall tubing.

The method by which this ash layer forms should also be considered. Theash particles as they strike the wall surface are in a molten state andfreeze as soon as they strike the walls. This continues until there isan ash buildup comprised of lightly bonded ash particles. As thisbecomes thicker the temperature of the outer layer increases so that thenew ash particles impinging thereon are cooled less slowly and tend toform a sintered or vitrified layer. As additional ash collects on thesurface the surface temperature becomes high enough to permit the ash toliquify in the form of fluid slag. Since most coal ash is a mechanicalmixture of many compounds, the fluid temperature of the ash is not welldefined and the wall deposit exists as a layer ranging from looselybonded ash at the tube surface through the vitrifled layer of solid ash,and then through a range of viscous semi-fluid to fluid slag on theouter surface which is immediately adjacent to the furnace cavity.

Where high heat absorption rates exist, particularly in the burner zone,there is a great tendency for the formation of this vitrified layeralong with the fluid outer layer. This is so because at the high heatabsorption rate the outer surface of the slag reaches the fluidtemperature with a relatively thin insulating layer of ash.

conventionally the ash layer on the furnace walls is removedperiodically by conventional well-known wall type soot blowers such asillustrated in US. Patent No. 2,662,241. These soot blowers operate byinserting a nozzle through the wall so that it blows from a position 1/2 to 2 inches on the furnace side of the crown of the furnace Walltube, and in a direction almost parallel to the furnace wall. The jet ofcleaning medium tends to blow against and across the slag layer toremove the slag.

A soot blower of this type is very effective on the loosely bonded ashparticles which comprise the earliest forma- 3,273,543 Patented Sept.20, 1966 tion in the burner zone and in lower heat absorption zonescomprise the total formation. However, when the vitrified layer forms,the efficiency of these soot blowers decreases. If the soot blower isable to penetrate the vitrified layer, it may then operate 011 the edgeof the remaining slag layer so that it is peeled back by the action ofthe jet which works on the remaining edge of the existing slag layer.The nozzle so inserted is rotated throughout 360 to effect cleaning ofthe general furnace wall area.

When a wall type soot blower is operated from a location very close tothe furnace wall tubes, there is a considerable problem with tubeerosion where the jet strikes the tubes. For this reason it has been thepractice to operate these wall blowers with the centerline of the nozzle1 /2 to 2 inches away from the tube walls. By operating a wall blowerwith a nozzle in this location a reasonable blowing pressure may be usedsuch as psi. so that a reasonable cleaning radius may be obtained. Byinserting the nozzle even farther through the wall a still increasedblowing pressure could be used without tube erosion damage and anincreased radius of cleaning obtained. This increased radius is effectednot only by the increased jet velocity but also by the lack of drag onthe jet flow which is due to the friction against the wall when blowingvery close to the wall. However, by blowing from such a location,cleaning would not be effected in the area immediately adjacent the wallblower. Where the only ash on the wall is a loosely bonded ash this wallblower would be effective for cleaning the wide range area while leavingan ash layer near the wall blower. However, where the slag layer hasbuilt up so that a vitrified layer is formed, the jet will frequently beunable to penetrate the vitrified layer at the distance from the jetwhere it comes in contact with the wall, and it would therefore beineffective in cleaning even a wide range area.

Accordingly there are two aspects of my invention which are ofconsiderable importance. When used in a section of a furnace which isheavily slagged and where there is a layer of vitrified ash formed, myinvention operates so that the ash and slag layer immediately adjacentthe wall blower is first removed. The conventional wall type soot bloweris then operated from either a normal location or from one more remotefrom the wall. The removal of the slag and ash immediately adjacent thewall blower permits the cleaning jet from the conventional blower tooperate on the edge of the remaining slag layer so that it may be peeledback from the wall avoiding the problem of attempting to penetrate theslag layer at a distance remote from the nozzle. Where the ash layer isformed of loosely bonded ash particles, my invention is effective toincrease the cleaning area of the conventional wall type soot blower.Since the area immediately adjacent the wall blower is cleaned either byfixed deslaggers or by operating the retractable blower at a locationextremely close to the wall with a reduced blowing pressure, the nozzlemay be operated from a location well within the furnace without fear ofmissing the area immediately adjacent the nozzle. The wall blower maythen be operated with extremely high blowing pressure with no fear oftube erosion so that the cleaning radius may be greatly increased.

It is an object of my invention to effect cleaning of a larger area ofthe furnace Walls with a wall blower which operates by directing a jetof cleaning medium across the furnace Wall surface.

It is a further object to provide a method and apparatus whereby wallblowers of the type which direct a jet of cleaning medium across thefurnace wall surface can be made effective in areas of heavy slagging.

Other and further objects of the invention will become apparent to thoseskilled in the art as the description proceeds.

Wih the afore-rnentioned objects in view, the inven tion comprises anarrangement, construction and combination of the elements of theinventive organization in such a manner as to attain the resultsdesired, as hereinafter more particularly set forth in the followingdetailed description of an illustrative embodiment, said embodimentbeing shown by the accompanying drawings wherein:

FIG. 1 is a side elevation of a vapor generator indicating general wallblower locations;

FIG. 2 is an elevation of a section of the furnace wall in the locationof a furnace wall blower which has fixed deslaggers associatedtherewith;

FIG. 3 is a sectional plan view through the same portion of the furnacewall;

FIG. 4 is a sectional elevation through a furnace wall illustrating awall blower operating with a nozzle position extremely close to thefurnace wall surface; and

FIG. 5 illustrates a sectional elevation through a furnace Wall with thejet operating from a location well within the furnace.

Referring to the illustration of FIG. 1, the walls 2 of the furnace 3are lined with parallel furnace wall tubes 4. These tubes convey waterto be heated from the lower headers 5 and 6 to the upper headers 7 and 8from which steam is released and conveyed through additional steamheating surface (not shown). Coal is introduced through burners 9 withcombustion occurring in the furnace 3 and the gas passing out to exhaustthrough the flue 10.

Conventional short retractable rotating type wall blowers 12 are locatedin the furnace walls at various locations. Blowers of this type areillustrated in US. Patent 2,662,241. A fixed deslagger 13 is locatedimmediately adjacent and on each side of the wall blower.

This arrangement of a rotating wall blower in conjunction with the fixeddeslaggers is illustrated in more detail in FIGS. 2 and 3. The paralleltubes 41 have bars 14 welded between adjacent tubes forming what isgenerally known as a web wall construction. Steam is delivered to thesoot blower through supply pipe 15 and is controlled by the operation ofvalve 17. The steam passes through the wall blower operating box 18.When the wall blower is activated, the blower tube 19 is advanced intothe furnace and steam is then delivered through operating box 18 andnozzle 20 blowing essentially parallel to the furnace wall. Once thenozzle is in blowing position steam is admitted through the nozzle 20and the blower tube 19, and the nozzle is then rotated through 360degrees. The wall blower may be operated so that the nozzle blowsthroughout the full are or for only a preselected portion of the arc.The nozzle once inserted may also be operated so as to make multiplerotations if desired.

A wall blower sealing box 22 is installed as part of the inner casing ofthe furnace and prevents furnace gases from leaking outward or air fromleaking inward through the tube openings required when the tubes areoffset for the wall blower. Immediately adjacent the wall blower fixeddeslaggers 23 such as those described in my copending application SerialNo. 405,166, filed on even date herewith, are installed. Thesedeslaggers include a pressure chamber 24 located outside the furnace andsecurely fastened to the furnace wall tubes. The webs 14 have holes 25drilled through them in the area of the deslagger so that steam passesfrom the pressure chamber through the fins and impinges on a baffleplate 27. It is thereby directed upwardly and downwardly along thefurnace walls at a location on the casing side of the crown of thefurnace wall tubes. Steam supply lines 28 to these deslaggers areconnected to the steam supply pipe 15 at a location downstream of valve17 so that steam is admitted to the pressure chamber at the same time itis admitted to the wall blower operating box 18.

Conventionally, a wall blower is inserted so that the centerline of theone inch diameter nozzle 20 is located about 1 /2 inches off the crownof the furnace wall tubes and at this point steam is passed through thenozzle directing a jet along the furnace wall tubes. As previouslydescribed, this jet has been frequently found ineffective where the ashhas formed so that there is a vitrified layer, and it has also beenfound that excessive blowing pressures tend to create tube erosion inthe area of the wall blower. In my invention, steam is admitted to thepressure chamber 24 and passes through the deslaggers 23 so that it isintroduced intermediate the tubes and the slag layer. The steam expandsunderneath this slag layer exerting a force on the slag layer which isperpendicular to the furnace walls and forces the slag and ash away fromthe walls, as described in my co-pending application Serial No. 405,166,cleaning the area immediately adjacent the wall blower. Consequently,when the jet passes from the wall blower and is directed across the wallof the furnace it is no longer impinging on top of the vitrified slaglayer but is operating on the edge of the remaining ash and slag layer.The jet is operative to exert a force on the edge of the remaining slagand ash so that it penetrates underneath it and even with normal blowingpressure effectively peels it back from the walls thereby cleaning thegeneral furnace wall area of the ash and slag surrounding the previouslylocally cleaned area.

Once the deslagger 23 is operated, steam delivery to it could bestopped, since the area is now cleaned. The only timing that isimportant is that the wall blower must operate, or continue to operateafter flow to the deslagger is initiated.

FIGS. 4 and 5 illustrate another method of achieving the two-stepcleaning of the furnace walls. Steam is admitted through supply pipe 35and is controlled by control valve 37. The steam passes into the wallblower control box 38 and operates to start moving the wall blower tube39. When the blower tube is inserted to such a point that the nozzle 40is at a location extremely close to the furnace wall, steam is admittedthrough the nozzle directing the steam jet 42 approximately parallel tothe furnace wall. The nozzle 40 has a diameter of about one inch and isoperated so that the centerline is about /2 to inch inside the furnace.The one edge of the jet 42 would then be almost flush with the crown ofthe furnace wall tubes. Inasmuch as operation of a wall blower so closeto the wall is likely to cause tube erosion, this first blow is made ata low pressure such as about p.s.i. Operation of the nozzle from thislocation is effective to reach beneath the slag layer locally and alsoto put the concentrated full force of the jet on the slag layerimmediately adjacent the wall blower. It will operate effectively toclean ash and slag away from that area immediately adjacent the wallblower, but it will not have carrying force to clean an extended area ofthe wall surface. The wall blower is rotated throughout 360 degreeswhile blowing through either the total are or a preselected portionthereof.

The nozzle is then further inserted as illustrated in FIG. 5 to alocation where the centerline of the nozzle is from 2 to 3 inches insidethe furnace wall and the blowing pressure is increased to between 250and 300 p.s.i. The steam jet 52 issuing forth from the nozzle at thisnew location operates on the remaining slag layer 53 and is directedacross the furnace wall so that it operates against the edge of theremaining slag layer. The jet penetrates underneath the ash and slag andis effective in peeling it back from the furnace walls. Whileconventionally a wall blower would operate with a blowing pressure ofabout p.s.i. from a location about 1 /2 inches inside the furnace fromthe furnace wall, my wall blower operates with a pressure of 250 to 300p.s.i. at a location between 2 and 3 inches inside the furnace from thefurnace wall. As a result of this higher blowing pressure and as aresult of the reduction in drag on the jet by the furnace wall, mymethod of cleaning the slag off the furnace walls is effectivethroughout a radius substantially greater than that of conventional wallblowers.

My invention is not limited to cooperation with conventional wallblowers, but may be used in conjunction with any blower which operatesby directing a jet of cleaning medium across furnace Walls to cleanthem. For instance, the jet may be directed across the front wall of afurnace from a location in the side Wall, adjacent the front wall.

I claim:

1. In a vapor generator having a furnace, tubes lining the walls of saidfurnace, means for burning an ash bearing fuel within said furnacewhereby ash collects on the tube lined walls of the furnace, and meansfor directing a jet of cleaning medium along at least a portion of afurnace wall, the method of cleaning ash off the walls of said furnacecomprising: burning fuel within the furnace and forming a layer of ashand slag on the walls thereof; removing ash from co-planar tubes lininga wall of the furnace, in a limited area immediately adjacent the jetmeans; thereafter directing the jet of cleaning medium across saidco-planar tubes lining said furnace wall so that it operates against theedge of the remaining ash layer whereby the ash beyond said immediatelyadjacent area is removed.

2. In a vapor generator having a furnace, tubes lining the walls of saidfurnace, means for burning an ash hearing fuel within said furnacewhereby ash collects on the tube lined Walls of the furnace, and meansfor directing a jet of cleaning medium along at least a portion of afurnace wall, the method of cleaning ash off the walls of said furnacecomprising: burning fuel Within the furnace and forming a layer of ashand slag on the walls thereof; removing ash from co-planar tubes lininga wall of the furnace, in a limited area immediately adjacent the jetmeans; thereafter directing the jet of cleaning medium across saidcoplanar tubes lining said furnace wall so that it operates against theedge of the remaining ash layer, and rotating the jet through apreselected arc, whereby the ash in the general area is removed.

3. In a vapor generator having a furnace, tubes lining the walls of saidfurnace, means for burning an ash bearing fuel within said furnacewhereby ash collects on the tube lined walls of the furnace, retractablerotating wall blowers located in the walls of said furnace, the methodof cleaning ash off the walls of said furnace comprising: burning fuelwithin the furnace and collecting a layer of ash on co-planar tubeslining a wall thereof; removing ash from the walls of the furnace, in alimited area immediately adjacent a Wall blower location; thereafteroperating the corresponding retractable rotating wall blower byinserting it and rotating it throughout its blowing are at such alocation that the wall blower operates to clean said co-planar tubeslining said furnace wall whereby the ash surrounding said immediatelyadjacent area is removed.

4. In a vapor generator having a furnace, tubes lining the walls of saidfurnace, means for burning an ash bearing fuel within said furnacewhereby ash and slag collect on the tube lined Walls and having meansfor directing a jet of cleaning medium along at least a portion of afurnace wall, the method of cleaning ash and slag off the tube linedwalls comprising: introducing cleaning medium immediately adjacent saidjet means and intermediate co-planar tubes lining a Wall and the ash andslag layer thereon, whereby ash and slag in the area immediatelyadjacent the jet means are removed; subsequently directing a jet ofcleaning medium across said co-planar tubes lining said furnace wall sothat it operates against the edge of the remaining ash and slag layer toremove ash and slag from an extended area.

5. The method of claim 4 including also rotating this jet throughout apredetermined arc to effect the desired cleaning of the general area.

6. In a vapor generator having a furnace, tubes lining the walls of saidfurnace, means for burning an ash bearing fuel within said furnacewhereby ash and slag collect on the tube lined walls and having aretractable type rotating wall blower located in a furnace wall, themethod of obtaining increased wall cleaning comprising: introducingcleaning medium immediately adjacent said wall blower and intermediateco-planar tubes lining the furnace wall and ash layer thereon, wherebyash and slag in the area immediately adjacent the wall blower areremoved; subsequently operating said Wall blower including directing ajet of cleaning medium essentially parallel to the wall surface alongthe furnace side of said co-planar tube lined wall surface to remove ashand slag from an extended area; and rotating this jet throughout apredeter mined arc to effect the desired cleaning of the general area.

7. In a vapor generator having a furnace, tubes lining the walls of saidfurnace, means for burning an ash bearing fuel within said furnacewhereby ash and slag collect on the tube lined walls and having aretractable type rotating wall blower located in a furnace wall, themethod of obtaining increased wall cleaning comprising: introducingcleaning medium immediately adjacent said wall blower and intermediateco-planar tubes lining the furnace wall and ash layer thereon, and in adirection essentially parallel to the furnace wall, whereby ash and slagin the area immediately adjacent the wall blower are removed;subsequently operating said wall blower including directing a jet ofcleaning medium essentially parallel to the wall surface from a locationslightly on the furnace side of said co-planar tubes to remove ash andslag from an extended area, and rotating this jet throughout apredetermined arc to effect the desired cleaning of the general area.

8. In a vapor generator having a furnace, tubes lining the walls of saidfurnace, and means for burning an ash bearing fuel within said furnacewhereby ash and slag form on the tube lined walls, the method ofobtaining increased wall cleaning comprising: projecting a jet ofcleaning medium approximately parallel to a co-planar tube lined furnacewall surface from a location Within the furnace extremely close to thefurnace wall surface; rotating the jet at this location through apredetermined arc whereby the area immediately adjacent the soot blowerlocation is cleaned; projecting a jet of cleaning medium essentiallyparallel to the co-planar tube lined furnace wall from a locationfarther inside the furnace from the furnace wall surface; and rotatingthe jet at this location through a predetermined arc to effect thecleaning of the general area.

9. In a vapor generator having a furnace, tubes lining the walls of saidfurnace, and means for burning an ash bearing fuel within said furnacewhereby ash and slag form on the tube lined walls, the method ofobtaining increased Wall cleaning comprising: projecting a jet ofcleaning medium approximately parallel to a co-planar tube lined furnawWall surface from a location within the furnace extremely close to thefurnace wall surface at a preselected blowing pressure; rotating the jetat this location through a predetermined arc whereby the areaimmediately adjacent this location is cleaned; projecting a jet ofcleaning medium essentially parallel to the co-planar tube lined furnacewall from a location farther inside the furnace from the furnace wallsurface at a higher blowing pressure; and rotating the jet at thislocation through a predetermined arc to effect the cleaning of thegeneral area.

10. In a vapor generator having a furnace, tubes lining the walls ofsaid furnace, means for burning an ash bearing fuel within said furnacewhereby ash collects on the tube lined walls and having a retractabletype rotating wall blower located in a furnace wall, the method ofobtaining increased wall cleaning comprising: inserting the wall blowerand projecting the cleaning jet approximately parallel to co-planartubes lining the furnace wall from a location within the furnaceextremely close to the co-planar tubes; rotating the jet at thislocation through a predetermined arc whereby the area immediatelyadjacent the wall blower location is cleaned; further inserting theblower and projecting the jet essentially parallel to the co-planartubes lining the furnace wall from a location well within the furnace;and rotating the jet at this location through a predetermined arc toeffect the cleaning of the general area.

11. In a vapor generator having a furnace, tubes lining the walls ofsaid furnace, means for burning an ash hearing fuel within said furnacewhereby ash collects on the tube lined walls and having a retractabletype rotating wall blower located in a furnace wall, the method ofobtaining increased wall cleaning comprising: inserting the wall blowerand projecting the cleaning jet approximately parallel to the furnacewall surface from a location extremely close to the furnace wall surfaceat a preselected blowing pressure; rotating the jet at this locationthrough a predetermined arc whereby the area immediately adjacent thewall blower location is cleaned; further inserting the wall blower andprojecting the jet essentially parallel to the furnace walls from alocation well within the furnace at a higher blowing pressure; androtating the jet at this location through a predetermined arc to effectthe cleaning of the general area.

12. In a vapor generator having a furnace, co-planar tubes lining a wallof said furnace, and means for burning an ash bearing fuel within saidfurnace whereby ash and slag collect on the tube lined wall, anapparatus for clean ing ash and slag off the tube lined walls of thefurnace comprising: means for projecting a jet of cleaning medium acrossat least a portion of the co-planar tube lined furnace wall from apreselected location, means for introducing cleaning medium intermediatethe co-planar furnace wall tubes and the slag layer thereon, immediatelyadjacent said preselected location; and means to effect the projectionof the jet of cleaning medium after the introduction of cleaning mediumintermediate the furnace Wall tubes.

13. In a vapor generator having a furnace, co-planar tubes lining a wallof said furnace, means for burning an ash bearing fuel within saidfurnace whereby ash and slag collect on the tube lined wall and having aretractable type rotating wall blower located in a furnace wall, anapparatus for improving the effectiveness of the wall blower comprising:means for introducing the cleaning medium intermediate the co-planartubes which the wall blower cleans and the slag layer thereon,immediately adjacent the wall blower location; and means to effect theintroduction of cleaning fluid in this location before the wall bloweris rotated throughout its final cleaning are.

14. In a vapor generator having a furnace, co-planar tubes lining a wallof said furnace, and means for burning an ash bearing fuel within saidfurnace whereby ash and slag collect on the tube lined wall, anapparatus for cleaning ash off the tube lined walls of the furnace comprising: means for projecting a jet of cleaning medium across at least aportion of the tube lined furnace wall from a preselected location, andmeans for introducing a gaseous cleaning medium intermediate adjacenttubes in a direction essentially parallel to said co-planar tubes at alocation between a plane defined by the furnace side of said co-planartubes and a plane defined by the opposite side of said co-planar tubesimmediately adjacent the jet means.

15. In a vapor generator having a furnace, co-planar tubes lining a wallof said furnace, and means for burning an ash bearing fuel within saidfurnace whereby ash and slag collect on the tube lined wall, anapparatus for cleaning ash off the tube lined walls of the furnacecomprising: means for projecting a jet of cleaning medium across atleast a portion of the tube lined furnace wall from a preselectedlocation, means for introducing a gaseous cleaning medium intermediateadjacent co-planar tubes in a direction essentially parallel to theco-planar tubes being cleaned at a location between a plane defined bythe centerlines of said co-planar tubes and a plane defined by thefurnace side of said c-o-planar tubes immediately adjacent the jetmeans, and means to effect the projection of the jet of cleaning mediumafter the introduction of cleaning medium intermediate the furnace walltubes.

16. In a vapor generator having a furnace, co-planar tubes lining a wallof said furnace, means for burning an ash bearing fuel within saidfurnace whereby ash and slag collect on the tube lined wall and having aretractable type rotating wall blower located in a furnace wall, anapparatus for improving the effectiveness of the wall blower comprising:means for introducing a gaseous cleaning medium intermediate adjacentco-planar tubes in a direction essentially parallel to the furnace wallbeing cleaned at a location between a plane defined by the centerlinesof said co-planar tubes and a plane defined by the furnace side of saidco-planar tubes on opposite sides of said wall blower and immediatelyadjacent said wall blower.

17. In a vapor generator having a furnace, co-planar tubes lining a wallof said furnace, means for burning an ash bearing fuel within saidfurnace whereby ash and slag form on the tube lined wall and having aretractable type rotating wall blower located in a furnace Wall, anapparatus for improving the effectiveness of the wall blower comprising:means for introducing a gaseous cleaning medium intermediate adjacenttubes in a direction essentially parallel to said co-planar tubes of thefurnace wall being cleaned at a location between a plane defined by thecenterlines of said co-planar tubes and a plane defined by the furnaceside of said co-planar tubes at a plurality of locations on oppositesides of said wall blower and immediately adjacent said Wall blower.

References Cited by the Examiner UNITED STATES PATENTS 1,807,255 5/1931Rawson 122-391 1,944,324 1/1934 Howse et al. 122-392 FOREIGN PATENTS288,830 4/ 1928 Great Britain. 336,728 10/1930 Great Britain. 453,2059/1936 Great Britain.

References Cited by the Applicant UNITED STATES PATENTS 1,732,429 10/1929 Bell. 1,930,782 10/ 1933 Turner. 1,992,336 2/ 1935 Turner.2,027,495 1/ 1936 Turner. 2,662,241 12/1953 -De Mart.

CHARLES I. MYHRE, Primary Examiner.

1. IN A VAPOR GENERATOR HAVING A FURNACE, TUBES LINING THE WALLS OF SAIDFURNACE, MEANS FOR BURNING AN ASH BEARING FUEL WITHIN SAID FURNACEWHEREBY ASH COLLECTS ON THE TUBE LINED WALLS OF THE FURNACE, AND MEANSFOR DIRECTING A JET OF CLEANING MEDIUM ALONG AT LEAST A PORTION OF AFURNACE WALL, THE METHOD OF CLEANING ASH OFF THE WALLS OF SAID FURNACECOMPRISING: BURNING FUEL WITHIN THE FURNACE AND FORMING A LAYER OF ASHAND SLAG ON THE WALLS THEREOF; REMOVING ASH FROM CO-PLANAR TUBES LININGA WALL OF THE FURNACE, IN A LIMITED AREA IMMEDIATELY ADJACENT THE JETMEANS; THEREAFTER DIRECTING THE JET OF CLEANING MEDIUM ACROSS SAIDCO-PLANAR TUBES LINING SAID FURNACE WALL SO THAT IT OPERATES AGAINST THEEDGE OF THE REMAINING ASH LAYER WHEREBY THE ASH BEYOND SAID IMMEDIATELYADJACENT AREA IS REMOVED.